Toll service trunking system



June 23, 1931. v. s. THARP I TOLL SERVICE TRUNKING SYSTEM Filed April19, 1930 2 Sheets-Sheet 1 QREWNEMQQ UiE'ZH" ELThaP June 23, 1931. v. s.THARP TOLL SERVICE TRUNKING SYSTEM 2 Sheets-Sheet 2 Filed April 19, 1930v UI'ETH- EThax-F Patented June 23, 1931 l 'UNETED stares PATENT seer cavrorons. rHAnP, or nL'MnURsT, rumors, ASSIGNOR T0 n-nsnnvn HOLDING COM-PANY, or cmceec, rumors, A CORPORATION or DELAWARE TOLL SERVICE TRUNKINGSYSTEM Application filed April 19,

This invention relates to telephone systems generally, and particularlyto toll-service trunking apparatus and equipment for automatic telephonesystems.

In modern automatic telephone systems, it is the usual practice toprovide a separate train of automatic switches for use by the tolloperator in completing connections to sub scribers lines. These switchesare of the same general type as the switches used for localoservice,except that they are designed to provide greater transmissioneiiicie'ncy and more complete supervision. This switch train includes,essentially, a toll-transmission selector repeater and atoll orcombination localand-toll connector. One or more intermediate selectorsmay be interposed between the selector repeater and the connector.

A toll switch train of the above general type is disclosed in UnitedStates patent to Wicks No. 1,633,149, of June 21, 1927. It will benoted, that, in this case, the connector on seizing a line reverses thedirection of current flow over the incoming trunk to initiate theswitchover operation of the toll-transmission selector. A later andnioreetlicient type of toll switch train is disclosed in the copendingapplication of Tharp and l/Vicks, SerialNo. 225,063, filed October 1c,1927, on

which, incidentally, the present invention may-be considered as animprovement; In the latter case, the connector disconnects ts line relayfrom the trunk to initiate the switchover operation of thetoll-transmission selector. Line-seizure supervision is given to thetoll operator in both cases following the switchover operation, and theapparatus is placed in waiting condition. Due to this difference ineffecting the switchover, the transmission selectors of the two systemscannot be used interchangeably. In making additions to exchangesemploying the older type of equipment, it has, therefore, beenimpractical in the past to install the newer type of toll-transmissionselectors.

It may be further noted that the requirements for line-busy supervisionare not uniform throughout the telephone industry. In some telephonesystems an audible busy tone is used t6 notify the'operator of anall-trunks- 1930. SerialNo. 445,570.

busy condition or a busy called 'line. In other systems, a lampassociated with the operators cord circuit is flashed under theseconditions. It has, therefore, been customary to build a separate typeof switch train to meet each condition.

One of the features of the invention is the provision of atoll-transmission selector which will operate equally well withconnectors employing either of the previously-dcscribed methods ofeffecting the switchover.

Another feature is the provision of a toll switch train which can beused without alterations in'systems employing either of thepreviously-referred-to methods of line-busy supervision.

A still further feature is the arrangement whereby the operator receivesno line-seizure supervision when an all-trunksbusy condi tion isencountered or a busy line is connected with. lVith this arrangement,the operator may proceed with setting up the connection withoutlistening for busy tone as soon as the supervisory lamp lights.

The foregoing features, together with others not specifically mentioned,will be described in detail, reference being bad to the accompanyingdrawings comprising" Figs. 1 and 2.

Referring now to the drawings, in Fig. l is shown the calling end of aregular tollcord circuit 0. This cord circuit may be of the usual typeprovided with a polarized relay for controlling the supervisory signal.The toll-transmission selector S terminates the trunk line extendingfrom the toll board to an automatic exchange. This switch is of thewell-known Strowger type. having directive vertical motion and automaticrotary motion.

In Fig. 2 is shown, in skeleton form, an intermediate selector S1 and atoll connector C. The intermediate selector may be of any well-knowntype provided with a fourth wiper for extending a ring-controlconductor. The connector shown, is arranged only for toll operation,although similar connectors arranged for both local and tell operationsmay be used if desired.

In order that the features of the invention may be fully appreciated,the operations involved in setting up'a tollconnection to the substationT will now be described 1n detail.

It will first be assumed that a toll call for substation T has come intothe toll board over a toll line (not shown), and that the operator hasanswered this call by connecting the answering end of the cord O to thetoll line. After determining that the call is for the subscriber atsubstation T, the operator will insert the calling plug P of the cordcircuit into the jack of an idle toll-service trunk, for example, thejack J terminating the trunk comprising conductors 1 and 2. Key K willthen be actuated to the right, thereby bridging the calling device CDacross the talking conductors of the trunk. Line relay 11 oftransmission selector S has its lower windin g normally connected totrunk conductor 2 by way of T normally-closed contacts of relays 6. and4,

and this relay now operates over the loop through the cord c rcuit toground at normally-closed lower contacts of relay 4. Relay device.

11 closes a circuit for release relay 12 which operates and prepares theholding circuit and impulsing circuits for the switch.

7 After connecting with an idle toll-service trunk and actuating thedialling key, the operator will proceed to dial the number of the calledsubscribers line. At-the completion of the dialling, the operator willrestore the key to normal, thereby bridging polarized supervisory relay3 across the talking strands of the cord in place of the calling Thecalling device interrupts the loop over which relay 11 is operated, andthat relay responds in the usual way. Responsive S to the first digitdialled, relay 11 transmits a corresponding series of impulses tovertical magnet 16, which operates to step the wipers oi the switch tothe called level. Slow-to-v the series, and maintains its armaturesactuated throughout the series of impulses. Re-

lay 13, on operating, short circuits a winding of the repeating coil to.improve impulsing,

and also prepares a circuit for relay 15. This circuit is completed atoil-normal contacts 22 which close on the first vertical step of thewipers. Relay15 operates, completes a locking circuit for itself throughthe interrupter contacts of rotary magnet 17 and prepares a circuit formagnet 17. Shortly after the last impulse of the series, relay 13restores and completes a circuit for rotary magnet 17 which operates tostep the wipers in on the first set of contacts of the called level. Magnet 17 opens the circuit of relay 15 at the interrupter contacts, andthe relay'restores and in turn opens the circuit of the rotary magnet.In case the trunk terminating in the first set of contacts is busy, thetest wiper of the switch will encounter agrounded contact and relay 15will reoperate and again i close the circuit of rotary magnet 17 Magnet17 will operate to step the wipers to the next set of contacts, and willopen the circuit of relay 15 as in the previous instance. This testingand stepping operation will be repeated as often as the test wiperencounters grounded contacts. When an idle trunk is found, which may be,for example, the trunk comprising conductors 2528, the test wiper of theswitch will not find a ground and ,relay 14 will operate in series withrelay 15. Relay 14 was prevented from operating before, since itswinding was shunted by the ground on the test wiper. Relay 15 does notoperate in series with relay 14, which has a relatively high resistance.Relay 14 switches the connection of the test wiper from its lowerterminal to its upper terminal to complete a holding circuit and toprevent the reoperation of relay 15, disconnects the vertical magnetfrom the impulsing circuit, connects the talking and control conductorsthrough to the wipers, and completes a circuit for the lower winding ofdifferential ing of relay 4 upon the operation of relay 14.

Relay 4 is so constructed that, when its lower winding alone isenergized, or when its upper and lower windings are energized so thatthey cooperate, the armatures of the relay are actuated. At this time,however, the current How in the upper winding is in such a directionthat the windings oppose each oth r and the relay is prevented fromoperating.

The second series of impulses is now dialled and relayll responds, as intheprevious instance, and repeats the impulses over the loops to relay41 of selector S1. Relay 13 again operates during the series ofimpulses, 1

its only function at this time being to short circuit a winding of therepeating coilto improve impulsing. The line relay of selector S1responds in the usual way, and the wipers of this switch are raised tothe called level, whereon the switch operates to select an idle trunk,for example, the trunk comprising conductors 4447.

Selector S1 on switching through extends the control loop through toline relay 52 0f connector G. Relay 52 operatesover the loop andcompletes a circuit for relay 58 which operates and locks to groundoncontrol conductor 45. Referring back to transmission selector S, relay 4is still prevented from operating since the two windings oppose eachother. It will be noted also that during the transmission of the secondseries of impulses,

"relay i1 opened the circuits for both the upper and lower windings ofthis relay responsive to each impulse to prevent the relay from ra-i'sethe wipers of the switch to the called level. Relay 54: operates inresponse to the first impulse of the series, and maintains its armaturesactuated throughout the series of impulses, thereby maintaining thecircuit of the vertical magnet after oil-normal contacts 62' open on"the first vertical step of the wipers. Shortly after the'last impulse ofthe series, relay 54 restores and prepares a circuit for the rotarymagnet at its back contact.

Relay 11 oftransmission selector S and relay 520i connector respond tothe last series of impulses, the latter relay transmitting correspondingimpulses to rotary magnet 59 which is connected in series withslowto-release relay 56 Relay 56 energizes in response to the firstimpulse of the series and maintains its armatures actuated throughoutthe series of impulses, closing an auxiliary impulsing'cireuitindependent of the normally-closed contacts of busy relay 55, and alsopreparing the busy test circuit by connecting the test wiper through tobusy test relay by wayof normally-closed contacts of switching-throughrelay 57.

It will be assumed at this time that the called line'is idle, and thatthe busy test wiper, therefore, does not encounter ground on the testcontact of the line. WVhen relay 56 restores shortly after the lastimpulse of the series, the test wiper is again connected through theupper winding of relay 57 to ground on'the' release trunk conductor 46.Relay 57 operates over this circuit from battery through'the cut-oiirelay of the line switch associated with the called line. Relay 57 onoperating connects the talking conductors through to the wipers of theswitch, separate the control and release-trunk conductors and connectsthe test wiper to the latter conductor, completes a locking circuit foritself to the'release-trunk'conductor,and

opens the circuit of the busy test relay and the rotary magnet; v p

The-operation ofrelay 57 completes a circuit for relay '51, whichoperates and locks to ground on conductor 46. Relay'51 disconnectsthe'talking conductors to the switch from line-relay"'52.and' extendsthem through to the wipers, andalso'opens a point in the originalenergizing circuit of relay 53.

Returning now to the transmission selector S, the disconnection of theline relay of the connector from the talkingconductors of the trunkdestroys the circuit of the upper winding of relay 4 which now operatesits armatures under the influence of its lower winding alone. Relay 4locks to ground through oii-normal contacts 19, bridges alternatingcurrent responsive to relay 7 across the conductors of the trunk, andalso bridges both windings of line relay 11 across the trunk, reversingthe connections, however, so that the current flow over the trunk is nowin the reverse direction.

After dialling the last digit, the operator restores the dialling key tonormal as previously mentioned, thereby bridging polarized relay 3across the talking strands of the cord. Since the direction of currentflow over the trunk has now been reversed, relay 3 will operate andcomplete the circuit oi supervisory lamp L. Lamp L lights to give theline-seizure supervision.

A connection has now been established with the wanted line, but noringing current has been sent out due to the fact that ring-cut-oilrelay 53 has been locked up to control conductor-(t5. hen the operatoris ready to signal the called subscriber, key K of the cord circuit willbe actuated to the left, thereby applying ringing current to thetoll-service trunk to operate relay 7 of transmission selector S. Relay7 completes a circuit for relay 8 which operates, closes a temporaryholding circuit for line relay 11 of the transmission selector, andremoves ground from the control conductor by opening contacts 29. Relay53 of the connector now restores and completes the ringing circuit whichincludes its own upper winding. Ringing current with superimposedbattery is intermittently connected to the ringing circuit by ringinginterrupter RI to signal the called subscriber.

A ring-back tone is transmitted to the operator through condenser 67 andthe normallyclosed upper contacts of relay 53.

When the called subscriber answers, a direct current loop is closed overwhich relay 53 energizes and again locks to the control conductor, towhich, incidentally, ground has been reconnected following therestoration of the cord circuit ringing key. Relay 53 on operatingextends the loop from the called subscribers line, back over the talkingconductor of the intermediate selector and interconnecting trunks, tobattery-feed relay 5, which was connected up responsive to the operationof relay 4. Relay 5 feeds battery to the called subscriber and operatesover the called subscribers loop to close a circuit for relay 6. Relay 6on operating, connects ground to the control conductor to preventreapplication of ringing current to the called line as long as thecalled suhscribers receiver is 05 the hook, disconnects line relay 11 ofthe transmission selector from the talking conductors of thetoll-service. trunk, and closes.

a holding circuit for that relay. The disconnection of the line relay ofthe transm1s-- sion selector opens the ClI'CHllJOf the supervisory relayof the cord circuit, and that relay' restores and extinguishes thesupervisory lamp to give the answering supervision. Conversation may nowtake place in the usual way. 5

When the called subscriber hangs up, the operating loop of relay 5 isopened and that relay restores and opens the circuit of relay scriber byagain operating ringing key K to apply ringing current to thetoll-service trunk as in the previous instance;

' To release the connection the operator withdraws the plug of the cordfrom the jack thereby opening the circuit of relay 11 which restores andin turn opens the circuit of relay 12." Relay 12 restores, removesground from the release-trunk conductor, and completes a circuit forrelease magnet 18 including offnormalcontacts 23 which closed on thefirst vertical step ofthe wipers. The release magnet operates in theusual way to restore the wipers of the switch to normal position. Whenthe wipers reached normal position, the locking circuit of relay 4 isopened at off-normal contacts 19 and that relay restores thereby placingthe transmission selector in condition to receive the next call. Theintermediate selector S1 will release in the usual way followingtheremoval of ground from release-trunk conductor 27. Relays 51 and 57of connector C were-also held operated over the release trunk conductorand restore following the removal of ground from that conductor. Relay53 will restore assoon as the control conductor is opened following therelease'of relay 14 of the transmission selector. Relays 51 and 53complete a circuit for release magnet 60 of the connector, this circuitincluding off-normal contacts '61, which openwhen the wipers reachnormal position. All apparatus is now returned to normal condition andis in readiness to receive the'next call.

It will be recalled that the switchover op eration, that is theoperation of relay 1, was initiated by the disconnection of the linerelay of the connector when an idle line was connected with. In theevent that'transmission selector S is used to extend'a connection by wayof'a connector such as that disclosed in the previously-mentioned WVickspatent,

the operation will be somewhat different. Referring to the patent, itwillbe noted that when a called line is connected with, the connectionof the line relay; tothe trunkis reversed. In this case, the reversal ofcurrent flow over the trunk line will cause the two windingsof relay 4to cooperate, whereon the relay will energize and complete the switchover operation exactly as in the previouslydescribed connection.

I/Vhen a connection, such as hasjust been described, is extended to aprivate branch exchange, it is often desirable to recall thebranch-exchange operator after the branchexchange subscriber has hungup, but before the branch-exchange operator has pulled down theconnection. In this case, the toll operator will actuate the ringing keyof her cord circuit, thereby applying ringing current to thetoll-service trunk to operate relay 7. Relay 7 will close a circuit forrelay 8 which will operate in the usual way, and since the connectionhas not been pulled down at the branch exchange, relays 5 and 6 will beoperated and alternating current will beapplied directly to the talkingconductors at the transmission selector. This current willoperate aring-down relay in the branch-exchange cord circuit, which inturn willoperate the recall signal associated therewith.

In case the called-line had been a paystation line, it would. benecessaryv for the toll operator to either refund or collect the coindeposited to pay for the-connection. To do this, the operator wouldfirstactuate the collect-and-refund key K1 either to the leftor rightdepending upon whether the coin was to be returned or collected, andwould then operate ringing key K to apply high-potential current to thetalking conductors of the trunk. Relay 9, which has a very high resistance, operates from this current and completes a circuit for relay 10.Relay 1O operates and connects a bridge across the outgoing conductorsof the switch and also connects the bridgeto the trunk conductor towhichthe high-potential current is connected. This current is therebyextended over the two talking conductors of the interconnecting trunksandthe called line, and actuates the control relay at the paystationline.

lar system involved. Consider first the type r of system using tonesupervision, in which case the busy-tone transformer BT will beconnected'to the tone conductor 32 at contacts of terminal 33. Referringback to the description of the transmissionselector S, it will berecalled that rotary magnet 17 and control relay 15 alternately operatedand released until an idle trunk was found. In case no idle trunk isavailable, this stepping operation will continue until the wipers of theswitch are rotated to eleventh position whereon the test wiper willleave the last grounded contact and remove the shunt from relay 14.

Relay 14 will operate, close a point in the up- 7 contacts 24 also closewhen the wipers reach eleventh position, and the busy tone is applied tothe upper talking conductor of the switch and through the repeating coilto the operators set. Relay 4 will not operate since the circuits ofboth its windings are open.

' The current flow over the trunk will not be reversed and consequentlyno line-seizure supervision will be given. The failure of thesupervisory lamp to light will indicate to the operator that the calledline has not been connectedwith and she will, therefore, actuate herlistening key, whereon the busy tone will inform her that a busycondition has been encountered. Selector S1 on encountering anall-trunks-busy condition, will operate in substantially the same manneras the transmission selector to return a busy tone to the operator.

.It will be recalled that when connector C has responded to the lastseries of impulses, relay 56 energized in parallel with the rotarymagnet and connected busy test relay 55 to the test wiper. In case theline connected with is busy, relay 55 will operate over a circuitextending through the test wiper to the grounded test contact engaged,and when relay 56 restores, shortly after the last impulse of theseries, relay 55 looks to ground on the release-trunk conductor.Busy-tone conductor 32 is thereby connected through the normally-closedcontacts of relay 56 and front contacts of relay 55 to the upper talkingconductor of the switch by way of condenser 68. Relay 51 does notoperatesince its circuit is opened at contacts of relay 57, therefore, theline-seizure supervision is not given. The operator will again actuateher listening key and be advised by the busy tone that the called lineis engaged.

It will be noted' that only one busy-tone machine has been shown for theexchange, although, obviously, ifdesired, separate machines can be usedfor each rank of switches, for instance, to give one tone for analltrunks-busy condition and a different tone for. a line-busycondition.

In the event that the flash-busy supervision is. desired, terminal 33will be connected to interrupter I1 instead of to busy-tone transformerBT. When the transmission selector S encounters an all-trunks-busycondition as previously described, relay 4 will operate from the firstground impulse applied to conductor 32 over a circuit extending throughrotary oif-nor1nal contacts 21. Relay 4 will lock up in the usual wayand connect up battery-feed relay 5. The connection of line relay 11 tothe toll-service trunk will be reversed, as previously described, andpolarized relay 3 of the cord circuit will operate as before. Groundimpulses from the interrupter will now cause relay 5 to operateintermittently over a circuit including rotary offnormal contacts 24,front contacts of relay 14, back contacts of relays 8 and 10, frontcontacts of relay 4, and the upper winding of relay 5. Relay 5 onoperating will disconnect relay 11 from the trunk, thereby opening thecircuit of relay 3 which will restore and open the circuit of thesupervisory lamp. This operation will be repeated at intervals dependingon the rate at which interrupter I1 applies ground impulses to conductor32, and lamp L will consequently flash to give the operator busysupervision.

Selector S1 in encountering an all-trunksbusy condition will rotate tothe eleventh position, whereon the circuit of the upper winding of therelay 4 of the transmission selector will be opened, and that relay willoperate. Ground impulses will then be applied to the upper talkingconductor by way of rotary ottnormal contacts 43 which close when theswitch is in eleventh position and the supervisory lamp of the cordcircuit will be flashed as in the previous case.

When connector C encounters a busy line, busy relay 55 will operate asdescribed in the previous connection, and when relay 56 restores,shortly after the last impulse of the final series, the busy-toneconductor 32 will be extended to relay 51 by way of back contacts ofrelay 56 and front contacts of relays 55 and 52. Relay 51 will operatefrom the first ground impulse on the busy-tone lead and will lock toground on the release trunk, disconnecting the line relay in the usualway, and connecting the talking conductors through. Relay 4 of thetransmission selector will operate responsive to the disconnection ofline relay 52 of the connector, and

will reverse battery over the toll-service trunk in the usual way. Theground impulses from conductor 32. will now be applied to the uppertalking conductor of the connector, and over the interconnecting trunksto intermittently operate relay 5 which causes the supervisory lamptoflash as previously described.

The release of the apparatus when a busy condition is encountered, issubstantially the same as that described for a connection to an idleline.

What is claimed is:

1. In a telephone system wherein calls are extended to subscribers linesvia a switch train comprising a plurality of automatic switches, adouble-wound relay in the first switch of the train, circuits closedresponsive to the completion of the operation of said first switch fordifierentially energizing the two windings of said relay to maintain thesame unoperated, means for temporarily Opening said circuits during theoperation of succeeding switches of the train, and means for alteringthe circuit of one of said windings to operate said relay responsive tothe completion of the operation of the last switch of the train.

2; In a telephone system wherein calls are extended to subscribers linesvia a switch train comprising a plurality of automatic switches, aswitchover relay in the first switch of the train, an operating windingand an auxiliary winding for said relay, a circuitfor said operatingwinding closedresponsive to the completion of the operation of saidfirst switch, a circuit including said auxiliary winding for energizingthe same to oppose said operating winding closed responsive to thecompletionof the operation of said first switch, and means responsive tothe completion of the operation of the last switch of the train foraltering said second circuit to permit said relay to operate over saidfirst circuit.

3. In a telephone system, a toll selector, toll connectors, adouble-wound sw tchover relay in the selector, means for operating saidselector to seize an idle one of said connectors,

' circuits completed responsive to the seizure of an idle connector fordifferentially energizing the two windings of said relay whereby themagnetic flux of the two windings substantially balance each other, andmeans in the connector for openingone of said circuits to upset thebalanced condition of the relay and permit the same to operate.

4. In a telephonesystem, a toll switch train comprising a plurality ofautomatic switches adapted'to be successively operated to extend aconnection, a double-wound relay in t-he first switch, a local circuitfor energizing 'one of said windings closed responsive to the completionof the operation of the first switch, a circuit for energizing the otherwinding of the relay to oppose said first winding, said circuitextending to successive switches of the train, and means in the lastswitch of the train for opening said last. circuit topermit said relayto operate. 7 I I 5. In a telephone system, two automatic switches, adifferentially-wound relay in the first switch, a double-wound linerelay in the second switch, means for operating the first switch toextend a connection to the second switch, a circuit including onewinding of said difierential relay and the two windings of said linerelay in series closed responsive to the completionof theoperation ofthe first switch, a local circuit for the other winding of saiddifierential relayclosed simultaneously with the closureof said firstcircuit, means pletionof the operation of the selector fordifierentially energizing the two windings of said relay,'means in theconnector responsive to the completion of the operation thereof foropening one of said circuits to permit said relay to operate, and meanscontrolled by said relay for reversing the direction of current fiowover the trunk line.

7 In a telephone system wherein connections are extended fromatollswitchboard to subscribers lines via atoll-service trunk line and.a toll switch train comprising a plurality of automatic switches, adouble-wound switchover relay in the first switch of the trainmaintained unoperated during the setting up ofa connection by having itstwo windings difi'erentially energized, means for opening the circuit ofone winding of therelay responsive to the connection being extended to asubscribers line, and a supervisory signal at the switchboard controlledby said relay. V

8. In atelephone system wherein connections are extended from a tollswitchboard to subscribers lines via a toll-service trunk line and atoll switch train comprising a plurality of automatic switches, adouble-wound switchover relay in the first switch of the trainmaintainedunoperated during the setting up of a connection by having itstwo windings difierentially energized, means for opening the circuit ofone winding responsive to the connection being extended to a subscribersline, and a battery-feed bridge in the first switch connected up by saidrelay to feed talking current to the called line. I

9. In a toll transmission selector adapted to cooperate with connectorswhich either open or reverse the direction of current flow over acontrol circuit whena called line is connected with, a control circuitover which a current How is maintained during the setting up of aconnection, and a switchover relay operative responsive to either theopening of or the reversal of current flow over said control circuit. Ir a W 10. In a toll transmission selector adapted to cooperate with tollconnectors which either open or reverse the direction of current flowover a control circuit when a called line is connected with, a controlcircuit over which a current flow is maintained while the selector is inoperating condition, and a relay operated responsive either to theopening of or the reversal of current flow over said control circuit forswitching over the selector from operating condition to talkingcondition.

11. In a toll transmission selector adapted to cooperate with tollconnectors which either open or reverse the direction of current flowover a control circuit when a called line is connected with, a controlcircuit over which a current flow from an external feeding bridge ismaintained during the setting up of a connection, a local currentfeeding bridge, and a switchover relay operated responsive to theopening of or the reversal of current flow over the control circuit forconnecting said local bridge to said circuit.

12. A toll selector, a signal-control relay and a battery-feed relay forthe selector, a busy signal terminal, a source of tone and a source ofinterrupted current either of which may be connected to said terminal,means for operating theselector to hunt for an idle trunk, meansresponsive when no idle trunk is available for applying a tone to atalking conductor of the switch provided said tone source is connectedto said terminal, and means for operating and locking said signalcontrol relay and for intermittently operating said battery-feed relayprovided said second current source is connected to said terminal.

13. In a tool selector, incoming trunk conductors, a battery-feed relay,a signal terminal, two sources of busy signalling current either ofwhich may be connected to said terminal, means for operating theselector, and means responsive when the selector encounters anall-trunks-busy condition for applying a characteristic tone to one ofsaid trunk conductors provided said first current source is connected tosaid terminal and for intermittently operating said relay providedsaidsecond tone source is connected to said terminal.

14. In a telephone system, a trunk line terminating in a toll selector,a line relay for the selector bridged across the talking conductors ofthe trunk, a signal terminal, two

sources of current either of which may be connected to said terminal,means for applying a characteristic tone to said trunk line providedsaid first current source is connected to said terminal, and means forintermittently disconnecting said relay from the trunk line providingsaid second current source is connected to said terminal.

15. In a toll connector, incoming trunk conductors, a signalcontrolrelay, a signal terminal, two sources of signal current either ofwhich may be connected to said terminal, means for operating saidconnector to extend a connection to a called line, and means re-

